Rabbit acquisitions.

<p><b>(a, b)</b> Axial TrueFISP slices of different rabbits showing the improved uniformity achieved with the proposed coil. <b>(c, d)</b> Coronal SNR maps with selected rectangular regions of interest and corresponding mean values. The higher increase in SNR is visible at the ends of the coil.</p

Phantom acquisitions at the isocenter.

<p><b>(a, b)</b> SNR maps, computed from the Gradient Echo Multi Slice (GEMS) images of the mineral oil phantom, showing better uniformity and reduced SNR with the proposed coil. The small white circles show the areas with maximum and minimum pixel intensities. The subregions of interest (10x10pixels) used to calculate the uniformity were selected inside these circles. <b>(c, d)</b> SNR maps calculated from Fast Spin Echo Multiple Slice images of the water/NaCl/sugar phantom, showing increased SNR (41.8%) with the proposed coil in a selected circular ROI. The numbers in white are the corresponding average SNR computed inside these ROIs.</p

Mechanical design of the coil.

<p><b>(a)</b> CAD design and <b>(b)</b> picture of the coil assembly. <b><i>Q</i></b> and <b><i>I</i></b> are BNC terminals connected to the cable traps by RG-223 coaxial cables. Tuning and matching can be adjusted for each channel by means of the red and blue knobs attached to fiberglass rods extensions of the corresponding capacitors. A handle and a simple holding mechanism facilitate the installation and fastening of the coil into the magnet bore.</p

Electrical design of the coil.

<p><b>(a)</b> Schematic design with actual component values. The interfacing circuit of channel <b><i>Q</i></b> and the tuning capacitor of channel <b><i>I</i></b> (1-23p) are shown. The bold lines represent copper traces conforming the resonator. <b>(b)</b> PCB design with zoomed panel showing one parallel plate capacitor in transparency (black circle). The blue and red regions represent the copper sections on the inner and outer surfaces, respectively. <b>(c)</b> Picture of the resonator showing interfacing circuits (<b><i>Q</i></b> and <b><i>I</i></b>) and cable traps. <b>(d)</b> PCB design of the shield (one of four sections). The blue and red traces represent the gaps on the inner and outer copper surfaces, respectively. <b>(e)</b> Picture showing outer surface of the shield. The arrows show copper regions created to improve RF isolation.</p

Comparison between young (n_young = 19) and elderly (n_elderly = 14) subjects along with measurement errors.

<p>For each case, the corresponding 95% confidence interval for the mean test-retest difference (<i>CI</i>_<i>d</i>), estimated from the test-retest analysis (see section 3.1. Repeatability) was centered at the mean of each group, in order to assess whether the difference between young and elderly is larger than the test-retest errors or not. With all metrics within every spinal cord region (vertebral level or WM region), the difference in means between young and elderly was undistinguishable from measurement errors.</p

Comparison across vertebral levels and WM regions along with the measurement errors for the group mean (n = 33) and individual subjects.

<p>The red envelope represents the 95% confidence interval for the test-retest difference (CI_d), which assesses the measurement error magnitude of the group mean (in black). The orange envelope represents the MDC (Minimum Detectable Change), difference required to compare individual subjects (faded gray lines). Note that the group mean approaching the edges of the CI_d (red envelope) reflects an asymmetric confidence interval due to a non-null offset between test and retest (non-null mean test-retest difference, ). However, no offset was large enough to report a significant systematic bias between test and retest (see section 3.1. Repeatability, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189944#pone.0189944.t001" target="_blank">Table 1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189944#pone.0189944.t002" target="_blank">Table 2</a>).</p

Repeatability indexes used to assess the repeatability of metrics over all WM according to vertebral levels.

<p>Repeatability indexes used to assess the repeatability of metrics over all WM according to vertebral levels.</p

Test and retest maps in a young and an elderly subject at each vertebral level (mean across levels) along with the mean maps across the 33 subjects.

<p>All these maps are in the template space. Note that the color bar scale has been adjusted to the mean maps contrast. On a single-basis subject, one can observe a somewhat poor test-retest repeatability, within and across slices. However, despite this poor repeatability, the average maps (here, n = 33) are more consistent in terms of symmetry and tract-specific variations. For example, we can clearly distinguish higher MTV in the fasciculus cuneatus versus in the gracilis (dorsal column), which is in agreement with previous histology work [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189944#pone.0189944.ref001" target="_blank">1</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189944#pone.0189944.ref067" target="_blank">67</a>].</p

Comparison of significantly different vertebral levels (A) or WM regions (B) with differences larger than measurement errors.

<p>Comparison of significantly different vertebral levels (A) or WM regions (B) with differences larger than measurement errors.</p

Power analysis based on each metric WM values for a two-sample t-test between young and elderly subjects with a significance level of 5%.

<p>Power analysis based on each metric WM values for a two-sample t-test between young and elderly subjects with a significance level of 5%.</p